The present invention relates generally to injection molding systems using a heated nozzle disposed in a mold bore to inject melt into multiple mold cavities having multiple mold gates opening from the mold bore into the mold cavities, and more particularly to an improved heater assembly used in multi-cavity injection mold gating.
Injection molding is widely used for the manufacture of a variety of items, some of which have thin and delicate cross sections. These items can be molded in large quantities by using a single heated nozzle that extends into a single mold bore which feeds a number of mold cavities. These mold cavities typically have gates which extend through the mold block between the mold bore and the mold cavity, forming a melt flowpath to convey the injected melt from the bore to the mold cavities. These gates are very small in cross-section and therefore it is desirable to provide a sufficient and constant application of heat to the melt flow which is directed toward each mold gate to ensure that the melt remains fluid while passing through the gates into the mold cavities.
One previous construction of a heated multiple gate nozzle which directs the melt to multiple mold gates is shown in Canadian Pat. No. 976,314, in which a multi-gate heater is disclosed having an intricately milled nozzle face with a series of convex openings formed therein. Another construction such as that shown in U.S. Pat. No. 4,094,447 relies in part on a specific configuration of the mold bore which includes a raised portion of the bore which is generally complementary to the heater nozzle face to fill much of the open area in the bore to cut down on the amount of heat transferred to the mold block during operation. Such approaches require costly machining of both the heater ends and mold block mold bore.
The present invention is directed to an injection molding multi-gate heater assembly construction which is less costly to manufacture in that it does not require extensive machining of the heater nozzle face or of the mold bore, and which has improved heat transfer and reduced heat loss capabilities.
In a multi-gate molding heater assembly constructed in accordance with the present invention, an elongate heated member having opposing inlet and outlet ends is adapted to fit in a mold bore. The heater has a melt injection passage extending through its inlet which directs fluid melt along a body portion of the heated member to a lower member enlarged portion having a nozzle face thereon heated member. The nozzle face has a number of gate tips disposed around its periphery which tips extend downwardly from the nozzle face and away from the heated member body portion to a position in registration with multiple mold gates located in the mold bore. A recess is formed between the gate tips and the mold bore and acts as a melt accumulation area for the initially injected melt to solidify in such that it insulates the subsequently injected melt from the cooler temperatures of the mold block surrounding further the mold bore.
Accordingly, it is a general object of the present invention to provide an improved heater assembly for use in injection molding systems having multiple gates.
Another object of the present invention is to provide a heated sprue bushing having a central melt injection passage which terminates in a bushing nozzle face having multiple gate tips peripherally disposed thereon which direct the melt to the mold bore gates.
It is another object of the present invention to provide a heated torpedo for insertion into a mold bore having a plurality of mold gates defining melt passages to mold cavities disposed in the mold bore wherein the torpedo has multiple gate extension tips disposed thereon in alignment with the mold bore gates.
It is still yet another object of the present invention to provide an improved heater assembly adapted to fit within a mold bore having multiple gates leading to multiple mold cavities, the heater assembly having multiple gate tips peripherally disposed on a heater nozzle face which engage the mold gates, the gate tips defining a recess between the nozzle face and the mold bore for the accumulation of melt therebetween for insulating the heated melt from the mold bore.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.